Ibuprofen is an anti-inflammatory drug. This activity is based on its ability to inhibit the function of cyclo-oxygenase. Ibuprofen exists in two enantiomeric forms because of an asymmetric center alpha to the carbonyl group. In vitro studies have shown that ibuprofen is only active in the S-form enantiomer; conversion of the inactive R- to the active S-form in vivo has been postulated and supported by in vitro evidence. Previously, the study of ibuprofen metabolism was done by invasive means. Our approach is noninvasive and in vivo, using live rats in an NMR imaging instrument. The ibuprofen enantiomers are labeled at the C2 position with 13-C and 2-H, and the drug's 13-C NMR spectrum variations were followed from the liver region of the rat.